The primary goal of this epidemiologic project is to test the hypothesis that reduced sleep hours place middle-aged adults at increased risk of gaining weight and developing type 2 diabetes. Obesity and its health consequences are increasingly serious public health problems in the US. An alarming trend of higher body mass index has been well documented both from serial cross-sections of the population and from cohort studies. There is also evidence of decreasing sleep hours in adults of all ages in the US. This trend toward reduced sleep hours has received little attention: other than concern over accidents caused by sleepiness, there are no population data documenting adverse health consequences of reduced sleep. Are these two secular trends related? Prior work has shown that sleep restriction decreases glucose tolerance, reduces leptin levels and increases evening cortisol. Decreased carbohydrate tolerance and increased sympathetic tone are well-recognized risk factors for the development of insulin resistance, obesity and hypertension. This project will use a longitudinal design, adding wrist actigraphy, an objective and noninvasive measurement of sleep in the home, to an excellent ongoing cohort study of cardiovascular risk whose participants are now in midlife, the CARDIA study (Coronary Artery Risk Development in Young Adults). The wrist actigraphy measurements will be taken at two time points, both during the 4-5 year interval between clinical examinations of the cohort. The study will answer these questions (1) Does quantity of sleep predict change in weight among middle-aged adults over the course of 4 to 5 years? (2) Does quantity of sleep predict change in fasting glucose, fasting insulin, or resting blood pressure among middle-aged adults over the course of 4 to 5 years? (3) Are sleep duration and quality related to socioeconomic status or race? If this study finds our hypotheses to be correct, we will have identified an altogether unrecognized and modifiable social factor which is contributing to the obesity epidemic in the US, and perhaps also to socioeconomic differentials in obesity and type 2 diabetes.